Method and apparatus for mixing gas and liquid

ABSTRACT

THE INVENTION RELATES TO A METHOD OF MIXING A GAS WITH LIQUIDS IN A TUBULAR REACTOR BY FEEDING THE GAS AND THE LIQUIDS TO A MIXING zONE. THE INVENTION ALSO RELATES TO AN SEPARATUS FOR CARRYING OUT THIS METHOD. RAPID MIXING ID EFFECTIVE BY FEEDING A STREAM OF LIQUID TO THE MIXING ZONE THROUGH ONE OR MORE NOZZELS WHOSE AXS EXTEND IN THE SAME DIRECTION AS THE AXIS OF THE MIXING ZONE, IN INJECTED LIQUID HAVING A VELOCITY OF FROM 5 TO 100 M./S., WHILST A SECOND STREAM OF LIQUID OF MUCH LOWER VELOCITY IS INTRODUCED INTO THE REACTOR INLET ZONE SURROUNDING SAID NOZZEL. THE GAS IS FED TO THE MIXING ZONE THROUGH ONE   OR MORE GAS INLETS LOCATED NEAR THE ORIFIECES OF THE LIQUID NOZZELS. THE MEAN CROSS-SECTIONAL AREA OF THE MIXING ZONE BEARS A SPECIFIC RATIO TO THE CROSS-SECTIONAL AREA OF THE ORIFICES OF THE LIQUID NOZZLES AND THE LENGTH OF THE MIXING ZONE BEARS A SPECIFIC RATIO TO THE HYDROLIC DIAMETER THEREOF. THE METHOD AND APPARATUS ARE PARTICULARLY SUITABLE FOR CARRYING OUT REACTIONS IN WHICH SHORT RESIDENCE TIMES ARE DESIRABLE AND THE REACTION PRODUCTS MUST NOT RECONTACT THE STARTING MATERIALS.

METHOD AND APPARATUS FOR MIXING GAS AND LIQUID Filed Feb. 16, 1972United States Patent 3,833,719 METHOD AND APPARATUS FOR MIXING GAS ANDLIQUID Heribert Kuerten, Mannheim, Otto N agel, Neustadt, Rolf Platz,Mannheim, and Richard Sinn, Ziegelhausen, Germany, assignors to BadischeAnilin- & Soda-Fabrik Aktiengesellschaft, Ludwigshafen (Rhine), GermanyFiled Feb. 16, 1972, Ser. No. 226,808 Claims priority, applicationGermany, Feb. 19, 1971,

Int. Cl. 1301f 3/00 US. Cl. 423-659 7 Claims ABSTRACT OF THE DISCLOSUREThe invention relates to a method of mixing a gas with liquids in atubular reactor by feeding the gas and the liquids to a mixing zone. Theinvention also relates to an apparatus for carrying out this method.Rapid mixing is effected by feeding a stream of liquid to the mixingzone through one or more nozzles whose axes extend in the same directionas the axis of the mixing zone, the injected liquid having a velocity offrom to 100 m./s., whilst a second stream of liquid of much lowervelocity is introduced into the reactor inlet zone surrounding saidnozzles. The gas is fed to the mixing zone through one or more gasinlets located near the orifices of the liquid nozzles. The meancross-sectional area of the mixing zone bears a specific ratio to thecross-sectional area of the orifices of the liquid nozzles and thelength of the mixing zone, bears a specific ratio to the hydraulicdiameter thereof. The method and apparatus are particularly suitable forcarrying out reactions in which short residence times are desirable andthe reaction products must not recontact the starting materials.

The present invention relates to a method and apparatus for mixing gasand liquid in a tubular reactor.

In a number of chemical reactions involving gases and liquids, themixing operation constitutes an important factor. In industry, mixing isgenerally effected by means of mechanically driven stirrers of variousdesigns. However, leaks inevitably occur at the stirrer shaft,particularly in reactions carried out under pressure. It is thuspreferred to use' arrangements in which there are no moving parts. It isknown for example to mix a gas with a liquid by injecting a stream ofliquid coaxially into a mixing tube which is cylindrical over its entirelength or which has a short cylindrical neck followed by a conicallydiverging tube, the jet of liquid mixing, in the mixing tube, with astream of gas fed to the annular space between the liquid jet and thewall of the mixing tube. Such so-called ejector reactors are known, forexample, as Venturi absorbers in the chemical industry. It is frequentlynecessary to connect the relatively small ejector reactors to a largerreaction chamber for continuation of the reaction, which reactionchamber may be in the form of a bubble column for example. In a largenumber of reactions between a gas and a liquid, however, the degree ofgas/liquid mixing achieved in ejector reactors is inadequate for theprovision of satisfactory yields and conversions.

' We have now found that the mixing of gas and liquid in a tubularreactor by feeding a gas and liquid to a mixing zonemay beadvantageously carried out by feeding a stream of liquid to a mixingzone through one or more liquid nozzles whose axes extend in the samedirection as the axis of the mixing zone, the injector liquid having avelocity of from 5 to 100 m./s., whilst a second stream of liquid ofmuch lower velocity is introduced into the reactor inlet zonesurrounding said nozzles, the gas being fed to the mixing zone throughone or more gas inlets Patented Sept. 3, 1974 located near the orificesof the liquid nozzles and the mean cross-sectional area of the mixingzone being from 5 to 500 times as large as the cross-sectional area ofthe orifice of the liquid nozzle or the sum of the cross-sectional areasof the orifices of the liquid nozzles, whilst the length of the mixingzone is from 2 to 30 times as great as its hydraulic diameter.

In an advantageous embodiment of the method, spiral motion is impartedto the liquid flowing through the liquid nozzles before it emergestherefrom and/or spiral motion is imparted to the liquid/ gas mixture inthe mixing zone.

Using this method, high yields and also high space-time yields may beachieved. Since our novel method makes use of smaller tubular reactorsthan those employed in conventional methods, for example, for reactionsin bubble columns, the method of the invention involves considerablyless expense than prior art methods.

Our new method is .generally suitable for mixing gases and liquids inprocesses either for effecting exchange of matter or for inducing areaction between a gas and a liquid. It is particularly suitable forcarrying out chemical reactions between gases and liquids where rapidand thorough mixing is required. It will be appreciated that the gas andliquid need not be pure substances but may also be any desired mixturesof substances. In the method of the invention it is also possible to mixa gas with two different liquids, one of which is injected through anozzle while the other is fed to the reactor inlet zone surrounding thenozzle. The method of the invention is used to advantage in carrying outreactions between gas and liquid where the reaction product should notrecontact the starting materials. For example, the present method may beused for the absorption of chlorine in water or the reaction ofpropylene with aqueous chlorine solution to form propylenechlorohydride. When applying our method to said reactions, the reactionconditions generally used for such processes, for example catalyst,temperature and pressure, are not affected. However, the greater mixingrate and improved thoroughness of mixing achieved in our method increasethe reaction rate and thus improve the degree of conversion. It maytherefore be advantageous to determine new optimum process parameterssuch as average residence time, temperature, pressure and amount ofcatalyst used, since the optimum values hitherto found in an industrialprocess may now no longer apply due to the higher reaction rate obtainedin our method. Using this novel method, it is frequently possible tocarry out reactions between a gas and liquid at somewhat lowertemperatures and in many cases higher yields of reaction product areobtained. The method is advantageously used in the oxidation of organicand inorganic compounds with oxygen or oxygen-containing gases such asair, for example the oxidation of sodium sulfite in aqueous solutionwith air to form sodium sulfate.

The method of the invention is also advantageous for carrying ourprocesses for effecting the transfer of material, for example theabsorption of chlorine in water or the absorption of phosgene in organicsolvents such as methylene chloride.

It is an important feature of our method that a preferably relativelysmall stream of liquid is injected through a nozzle at a velocity offrom 5 to m./s. and preferably from 10 to 30 m./s. Whilst a second,preferably relatively large stream of liquid, is fed to the reactorinlet zone surrounding the nozzles at a considerably lower velocity thanthat of the injected liquid. In general, the ratio of injected liquid tothe liquid fed to the said inlet zone is from 1:1 to 1:50 and preferablyfrom 1:1 to 1:10. Advantageously, the velocity of the liquid fed to saidinlet zone is from 0.1 to 20 m./s. and preferably from 0.5 to 5 m./s.

The feed of liquid to the reactor inlet zone surrounding the nozzles maybe elfected through one or more feed lines and the actual number of suchfeed lines is not critical.

The average cross-sectional area of the mixing zone should be from 5 to500 times and preferably from to 100 times as large as thecross-sectional area of the liquid nozzle orifice or the sum of thecross-sectional areas of the liquid nozzle orifices, and the length ofthe mixing zone should be from 2 to 30 times as great as its hydraulicdiameter. The length and the hydraulic diameter of the inlet zone may bevaried within wide limits. The mixing zone generally has a constantcross-sectional or a crosssection which increases in the direction offlow, and. it may vary in design. In general, a cylindrical tube oralternatively a mixing tube having a short cylindrical neck followed bya conically diverging tube is used. The inlet zone may also vary indesign, although it generally takes the form of a cylindrical tube.

By the term hydraulic diameter of a zone we mean the diameter of acylindrical tube which has the same length as the zone in question andshows the same pressure loss when fluid is passed therethrough at thesame rate.

In the method of the invention, a single liquid nozzle or a plurality ofliquid nozzles, for example from 2 to 10 such nozzles, may be used.Where a plurality of liquid nozzles is used, these may be arranged in acircle or in one or more close groups. The gas is also fed through oneor more, for example from 2 to 10, gas nozzles, the number of gasnozzles and the number of liquid nozzles being the same or different.The gas is generally introduced in the proximity of the orifices of theliquid nozzles. The nozzle orifices may be in the form of, say, roundholes, slots or even annular gaps. The gas generally emerges from thenozzle(s) in the same direction as the jet(s) of liquid and the gasvelocity is convenient- 1y not higher than that of the jet(s) of liquid.In general, the velocity of the injected gas is from 5 to 50 m./s.Preferably, the gas and injected liquid are introduced through atwo-component nozzle, the liquid being fed through the central orificeof the nozzle whilst the gas flows through the annular gap coaxiallysurrounding the said central orifice.

In a preferred embodiment of the method, spiral motion is imparted tothe injected liquid before it leaves the nozzle and/or spiral motion isimparted to the liquid/gas mixture in the mixing zone. Spiral motion maybe imparted to the injected liquid for example by placing a twist guidein the form of a single-pitch or multiplepitch screw in the path of theliquid upstream of the nozzle outlet or by arranging for the liquid toflow into the feed line of the nozzle tangentially. Spiral motion may beimparted to the liquid/gas mixture in the mixing zone for example byimparting a twist to the slow outer stream also, for example byproviding a rifled inlet to said mixing zone. It is particularlyadvantageous to create a back pressure at the end of the mixing zone.This may be achieved, for example, by connecting a sufliciently highbubble column to the outlet of the mixing zone. Alternatively, anenergy-consuming system in the form of battle plates or centrifugalseparators may be placed downstream of the mixing zone. Another methodof creating a back-pressure is to insert a pressure-holding valvedownstream of the mixing zone. In general, the mixing zones are arrangedvertically, the gas and liquids being caused to flow upwardlytherethrough. Alternatively, the gas and liquid may be caused to flowdownwardly through vertical mixing zones or the mixing zones may bedisposed horizontally or in an inclined position, as desired.

The invention is further described with reference to nozzle outlet by 3,the liquid and gas nozzle inlets by 4 and '5 respectively, whilst thereference numeral. .6 -designates the liquid inlet to the inlet zone 7.The transition from inlet zone to mixing zone is conveniently gradual inorder to prevent the liquid flowing from the inlet zone to the mixingzone from detaching itself from the walls of these zones.

FIG. 2 illustrates a combination of the jet reactor with baffle plate 8disposed downstream; of the mixing zone and the use of a twist guide inthe path of the injected liquid.

FIG. 3 illustrates a combination of the jet reactor with a conventionalbubble column 10 having a gas outlet 11 and liquid outlet 12. In thiscase, the pet reactor serves as the gassing device for the bubblecolumn.

EXAMPLE 1 The reaction was carried out using a tubular reactor having adiameter of 20 mm. (see FIG. 1). The length of the mixing zone was 150mm. and the diameter of the liquid nozzle was 5 mm. The liquid nozzlewas coaxially surrounded by an annular gas nozzle.

The liquid passed through the liquid nozzle at a velocity of 20 m./s.consisted of 1.4 m. /hr. of an aqueous sodium sulfite solutioncontaining 600 moles/m. of sodium sulfite and 0.27 mole/m. of cobaltsulfate as catalyst. The reaction temperature was 20 C. and the pH wasadjusted to 9.2 m. /hr. of air (STP) were passed through the annularnozzle. A futher 2.0 m. /hr. of aqueous sodium sulfite solution of theabove concentration were passed to the inlet zone through a separateinlet. The slow stream of liquid had a velocity of 2.2 m./s. In theoxidation of the sodium sulfite to sodium sulfate, the conversion, basedon atmospheric oxygen, was 52%.

When the reaction was carried out in the above-described manner butwithout feeding liquid to the inlet zone through the separate inlet, theconversion was only 15% based on atmospheric oxygen.

EXAMPLE 2 EXAMPLE 3 The reaction was carried out as described in thefirst paragraph of Example 1, a bafiie plate having been placed at adistance of 20 mm. from the outlet of the mixing zone. The conversion ofsulfite to sulfate was 80%.

EXAMPLE 4 The reaction was carried out using a tubular reactor having adiameter of 20 mm. The length of the mixing zone was 200 mm. and thediameter of the liquid nozzle was 3 mm. The liquid nozzle was coaxiallysurrounded by an annular gas nozzle.

The liquid passed through the liquid nozzle at a veloc: ity of 15 m./s.consisted of 333 L/hr. of water, the

resulting jet of water being concentric with the mixing zone. A further667 l./hr. of water were fed to the inlet zone surrounding the nozzlesthrough a separate inlet at a lower velocity. 1.5 mfi/hr. of chlorine(STP) were fed" through the annular gas nozzle. The chlorine was com--pletely absorbed within the mixing zone and a satu-' ration of the waterwas achieved.

We claim:

1. A method of mixing a gas with liquids in a tubular reactor by feedingthe gas and liquids to a mixing zone, wherein a stream of liquid is fedto a mixing zone through one or more liquid nozzles whose axes extend inthe same direction as the axis of the mixing zone, the injected liquidhaving a velocity of from 5 to 100 m./s., while a second stream ofliquid is introduced at a velocity in the range of 0.1 to 20 m./s. andalso substantially slower than said injected liquids velocity into thereactor inlet zone surrounding said nozzle or nozzles, the gas being fedto the mixing zone through one or more gas inlets located near theorifices of the liquid nozzles and the mean cross-sectional area of themixing zone being from 5 to 500 times as large as the cross-sectionalareas of the orifices of said liquid nozzles, the ratio of said injectedliquid to said liquid of said second stream being in the range of 1:1 to1:50, and the length of the mixing zone is from 2 to 30 times as greatas its hydraulic diameter.

2. A method as claimed in claim 1, wherein spiral motion is imparted tothe liquid flowing through the liquid nozzle or nozzles before it leavessaid nozzle or nozzles.

3. A method as claimed in claim 1, wherein spiral motion is imparted tothe liquid/gas mixture in the mixing zone.

4. A method as claimed in claim 1, wherein back pressure is placed onthe liquid/gas mixture at the downstream end of the mixing zone.

5. A method as claimed in claim 4, wherein the velocity of the gas fedto the mixing zone is from 5 to 50 m./s. and also not higher than saidinjected liquids velocity.

6. A method as claimed in claim 4, said injected liquid being fedthrough a central orifice of the liquid nozzle and said gas beingsupplied as an annular gas stream about the liquid flowing from saidcentral orifice.

7. A process as claimed in claim 4, said injected liquid having avelocity of 10 to m./s., said second stream of liquid having a velocityof 0.5 to 5 m./s., and said gas fed to said mixing zone having avelocity which is not higher than said velocity of said injected liquid.

References Cited UNITED STATES PATENTS 2,747,974 5/1956 Felger 23--252 R2,361,150 10/1944 PetrOe 23252 R 2,798,794 7/1957 Muench et al. 23-252R3,755,452 8/1973 Sinn et al. 260-586B OSCAR R. VERTIZ, Primary ExaminerH. S. MILLER, Assistant Examiner US. 01. X.R.

